High-hardness powder metallurgy tool steel and article made therefrom

ABSTRACT

A tool steel alloy having a unique combination of hardness and toughness is disclosed. The alloy contains, in weight percent, about: wt. % C 1.85-2.30, Mn 0.15-1.0, Si 0.15-1.0, P 0.030 max., S 0-0.30, Cr 3.7-5.0, Ni+Cu 0.75 max., Mo 1.0 max., Co 6-12, W 12.0-13.5, V 4.5-7.5. The balance is essentially iron and usual impurities. The elements C, Cr, Mo, W, and V are balanced in this alloy such that −0.05≦ΔC≦−0.42 where ΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C. A powder metallurgy tool steel article made from consolidated alloy powder having the aforesaid weight percent composition provides a Rockwell C hardness of at least about 69.5 when heat treated.

This application claims the benefit of priority of U.S. ProvisionalApplication No. 60/117,820, filed Jan. 29, 1999.

FIELD OF THE INVENTION

This invention relates to tool steel alloys, and in particular, to ahigh speed tool steel alloy and a powder metallurgy article madetherefrom that has a unique combination of hardness and toughness.

BACKGROUND OF THE INVENTION

AISI Type T15 alloy is a known tungsten high speed steel alloy. The TypeT15 alloy is considered to be among the premium high speed tool steelgrades because it has a combination of hardness and wear resistance thatis superior to other high speed tool steel alloys such as Types M2 andM4. Type T15 alloy provides a hardness of about 66 to 67 HRC at roomtemperature. A higher carbon version of Type T15 alloy that is capableof providing a room temperature hardness of 67 to 68 HRC has been soldin the U.S. However, a demand has arisen in the tooling industry for ahigh speed tool steel alloy that provides greater combined levels ofhardness, including elevated temperature hardness, and wear resistancethan the known grades of high speed steel alloys, such as Type T15.

Currently there are essentially two types of materials that areavailable for the more demanding tooling applications such asmetal-cutting tools and gear hobs: conventional high speed tool steelsand cemented carbide materials. The known high speed steel alloys, evenwhen produced by powder metallurgy techniques, leave something to bedesired for extended tooling runs because tools manufactured from thosematerials lack sufficient wear resistance, room temperature hardness,and hot hardness. There is presently a trend in industry toward use ofdry machining as opposed to the use of cutting fluids because of thepotential environmental hazard associated with conventional cuttingfluids. Metal cutting tools are likely to be subjected to significantlyhigher operating temperatures when used in dry machining operations.Most of the known high speed steel alloys are not suitable for use indry cutting operations because their wear resistance and hardnessdegrades very rapidly under the extreme temperature conditions.

To avoid the limitations of the known high speed tool steels, oneapproach has been to produce cutting tools with a very hard surfacecoating to improve the service life of these cutting tools. Such acoating is typically applied by either physical vapor deposition (PVD)or chemical vapor deposition (CVD). Such coatings are typically harderthan about HRC 70, which is much harder than the base tool steel. Itwould be advantageous to provide a tool steel alloy having increasedhardness to back up the very high hardness coating.

Because of the disadvantages associated with the known high speed steelalloys as outlined above, cemented carbide materials have become veryattractive for making cutting tools. Cemented carbide materials providevery high hardness, both at room and elevated temperatures, and verygood wear resistance. Although cemented carbide tooling materialsprovide excellent hardness and wear resistance, they have severaldisadvantages. For example, carbide tooling is very expensive toproduce, not only because of the cost of making the carbide blanks, butalso because of the extra cost of forming the cutting tools from thoseblanks. In addition, carbide tools have very low toughness and specialcare must be taken to prevent fracture during service. Also, extremelyrigid machines must be used with carbide tooling, and therefore, a largeportion of existing cutting machines cannot be safely run with carbidetooling.

SUMMARY OF THE INVENTION

The alloy according to the present invention, and a consolidated powdermetallurgy article formed therefrom, resolve to a large degree severalof the problems associated with the known high speed tool steels andcemented carbide materials. In general, the invention provides a highhardness, high speed tool steel alloy having a unique combination ofhardness, hot hardness, and toughness. The broad, intermediate, andpreferred weight percent compositions of the alloy according to thisinvention are set forth in Table 1 below.

TABLE 1 Elmt. Broad Intermediate Preferred C 1.85-2.30 1.90-2.201.90-2.20 Mn 0.15-1.0  0.15-0.90 0.15-0.90 Si 0.15-1.0  0.50-0.800.55-0.75 P 0.030 max. 0.030 max. 0.030 max. S   0-0.30   0-0.30  0-0.30 Cr 3.7-5.0 4.0-5.0 4.25-5.00 Ni + Cu  0.75 max.  0.50 max. 0.50 max. Mo  1.0 max.  1.0 max.  1.0 max. Co  6-12  7-11  7.5-10.5 W12.0-13.5 12.25-13.5  12.5-13.5 V 4.5-7.5 5.0-7.0 5.0-6.5

The balance of the alloy is essentially iron and the usual impuritiesfound in commercial grades of high speed tool steels intended forsimilar types of service. The carbon content of the alloy according tothis invention is controlled such that the parameter ΔC is about −0.05to −0.42, better yet about −0.10 to −0.35, and preferably about −0.15 to−0.25. ΔC is calculated as follows.

ΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C

where ((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V)) is the carbon balance of thealloy, C is the actual carbon content of the alloy, and W, Mo, Cr, V,and C are given in weight percent.

Here and throughout this application, the term “percent” or the symbol“%” means percent by weight unless otherwise indicated.

DETAILED DESCRIPTION

At least about 1.85% carbon is present in this alloy to benefit the highhardness provided by the alloy in the hardened and tempered condition.Carbon combines with the carbide-forming elements in this alloy toproduce carbides that contribute to the excellent wear-resistanceprovided by the alloy. The alloy preferably contains at least about1.90% carbon. Too much carbon adversely affects the toughness providedby this alloy, and at very high levels, can adversely affect theattainable hardness of the alloy. Therefore, carbon is restricted to notmore than about 2.30% and preferably to not more than about 2.20% inthis alloy. Because carbon is depleted when carbides are formed in thealloy, the amount of carbon is controlled so that there is sufficientcarbon to permit the attainment of the desired hardness provided by thealloy as well as to permit the formation of an adequate volume of hardcarbide particles to provide the desired wear resistance. To that end weuse the factor ΔC described above whereby the amount of carbon presentin the alloy can be controlled to provide the unique combination ofproperties that are characteristic of this alloy.

This alloy contains at least about 0.15% manganese to benefit thehardenability of the alloy. In the resulfurized embodiment of the alloyaccording to this invention, manganese combines with sulfur to formmanganese-rich sulfides that are highly beneficial to the machinabilityof the alloy. Too much manganese causes brittleness in this alloy.Therefore, manganese is limited to not more than about 1.0% andpreferably to not more than about 0.90%.

At least about 0.15%, better yet at least about 0.50%, and preferably atleast about 0.55% silicon is present in this alloy to benefit thehardenability of the alloy and its hardness response. Silicon alsocontributes to the fluidity of the alloy in the molten state whichfacilitates the atomization of the alloy for powder metallurgyapplications. Too much silicon adversely affects the good toughnessprovided by this alloy. Therefore, the amount of silicon is restrictedto not more than about 1.0%, better yet to not more than about 0.80%,preferably to not more than about 0.75%.

This alloy may contain up to about 0.30% sulfur to form manganese-richsulfides which benefit the machinability of the alloy as describedabove. At least about 0.06% sulfur has been found to effective for thatpurpose. In order to form a sufficient quantity of sulfides to benefitthe machinability property, the amounts of manganese and sulfur presentin the alloy are selected to provide a Mn-to-S ratio (Mn:S) of about 2:1to 4:1, and preferably about 2.5:1 to 3.5:1. Sulfur adversely affectsthe toughness provided by this alloy and, therefore, it is restricted tonot more than about 0.30% in the enhanced machinability embodiments ofthis alloy. Where enhanced machinability is not needed, sulfur should bekept as low as possible. Therefore, in a non-resulfurized embodiment ofthis alloy, sulfur is restricted to not more than about 0.06%, betteryet to not more than about 0.030%, and preferably to not more than about0.020%.

At least about 3.7% chromium is present to benefit the hardenabilityprovided by this alloy. To that end the alloy preferably contains atleast about 4.0%, and better yet, at least about 4.25% chromium.Chromium combines with available carbon to form chromium carbides. Indoing so it depletes the alloy of carbon. Such carbon depletion tends toincrease the value of ΔC such that the hardness and toughness providedby the alloy are adversely affected. Therefore, chromium is restrictedto not more than about 5.0% in this alloy.

Cobalt is present in this alloy because it benefits both the roomtemperature hardness and the hot hardness provided by the alloy. Forthat purpose, the alloy contains at least about 6%, better yet, at leastabout 7%. and, preferably, at least about 7.5% cobalt. Too much cobaltcan adversely affect the good toughness provided by this alloy.Therefore, cobalt is restricted to not more than about 12%, better yetto not more than about 11%, and preferably to not more than about 10.5%in this alloy.

This alloy contains at least about 12.0% tungsten to benefit thesecondary hardness, wear resistance, and the hot hardness provided bythe alloy. If the amount of tungsten is too low, the value of ΔC becomestoo negative which adversely affects the hardness and toughness providedby the alloy. Accordingly, the alloy preferably contains at least about12.25%, and better yet, at least about 12.5% tungsten. When too muchtungsten is present in the alloy, the value of ΔC becomes too positivewhich adversely affects the hardness capability of the alloy. Therefore,tungsten is restricted to not more than about 13.5% in this alloy.

Vanadium contributes to the temper resistance and the secondaryhardening response that are characteristic of this alloy. Vanadiumcombines with available carbon to form vanadium carbides whichcontribute to the good wear resistance provided by this alloy. Thevanadium carbides also help control the grain size of the alloy duringthe austenitization heat treatment by pinning the grain boundaries. Forthese reasons, at least about 4.5% vanadium is present in this alloy. Wehave also found that when at least about 5.0% vanadium is present and ΔCis maintained within the aforesaid ranges, the alloy providesunexpectedly improved toughness at the elevated hardness levels that arecharacteristic of the alloy. Too much vanadium adversely affects thehardness and toughness provided by this alloy. More specifically,excessive vanadium can cause brittleness in this alloy. Also, ifvanadium is not properly balanced with carbon in this alloy, thehardness of the alloy will be adversely affected if there isinsufficient carbon to combine with vanadium. Therefore, vanadium isrestricted to not more than about 7.5%, better yet, to not more thanabout 7.0%, and preferably, to not more than about 6.5%.

A small amount of molybdenum may be present in this alloy insubstitution for some of the tungsten. Preferably, molybdenum isrestricted to not more than about 1.0% because too much causes ΔC tobecome more positive, which adversely affects the high hardness providedby the alloy.

The balance of the alloy is iron except for the usual small amounts ofimpurities that are present in commercial grades of high speed toolsteel alloys intended for similar service or use. More specifically,nickel and copper are restricted in this alloy to minimize retainedaustenite in the alloy after high temperature austenitizing heattreatment. Although up to 0.75% nickel or up to 0.75% Cu can be presentin this alloy, when both are present, the combined amount of nickel andcopper is restricted to not more than about 0.75%. Preferably, not morethan about 0.50% nickel-plus-copper is present in this alloy. Up toabout 0.1% magnesium and up to about 0.1% titanium can be present inthis alloy. In addition, the alloy may pick up nitrogen when it isatomized with nitrogen gas. However, it is expected that no more thanabout 0.12%, preferably not more than about 0.08% nitrogen is present innitrogen-atomized metal powder made from this alloy. Phosphorus isrestricted to not more than about 0.030%.

This alloy can be made by any conventional process known for making highspeed tool steels. Preferably, the alloy is produced by powdermetallurgy techniques. For example, a heat is melted and atomized,preferably with nitrogen gas to form a metal powder. The metal powder isscreened to the desired mesh size, blended, and consolidated to asubstantially fully dense billet or other shape. Consolidation iscarried out by any known process such as hot isostatic pressing, rapidisostatic pressing, or simultaneous compaction and reduction. Theresulting compact is then subjected to further mechanical working as bypress forging, rotary forging, or rolling.

EXAMPLES

In order to demonstrate the unique combination of properties provided bythe alloy according to this invention, 11 experimental heats wereprepared. The weight percent compositions of each heat are shown inTable 2 below.

TABLE 2 El. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ht. A Ht. B Ht. C Ht. DHt. E C 1.96 2.11 1.95 2.18 2.18 2.26 1.85 2.12 1.93 2.13 2.31 Mn 0.600.65 0.61 0.62 0.63 0.62 0.60 0.65 0.60 0.60 0.60 Si 0.65 0.64 0.67 0.660.65 0.65 0.63 0.63 0.64 0.64 0.65 P 0.008 0.006 0.008 0.008 0.007 0.0060.010 0.005 0.010 0.010 0.010 S 0.24 0.23 0.23 0.24 0.25 0.24 0.23 0.240.24 0.24 0.24 Cr 4.74 4.80 4.77 4.81 4.87 4.89 4.69 4.87 4.74 4.73 4.81Ni 0.26 0.20 0.24 0.21 0.20 0.20 0.27 0.20 0.26 0.25 0.25 Mo 0.19 0.220.20 0.22 0.22 0.22 0.20 0.24 0.20 0.20 0.20 Cu 0.06 0.06 0.06 0.06 0.060.06 0.06 0.07 0.06 0.06 0.07 Co 7.54 10.12 10.10 7.62 10.15 10.14 4.995.10 5.00 4.98 5.04 W 13.18 13.02 13.32 12.99 12.87 12.95 12.87 12.7812.82 12.97 13.17 V 4.95 6.15 5.13 5.19 5.29 5.76 5.02 6.09 5.04 4.975.08 N 0.069 0.080 0.082 0.072 0.075 0.083 0.07 0.089 0.08 0.075 0.07 ΔC−0.24 −0.15 −0.19 −0.41 −0.39 −0.37 −0.13 −0.17 −0.20 −0.41 −0.56

The balance in each case is iron and the usual impurities.

Examples 1 to 6 represent alloys within the scope of the presentinvention and Heats A to E are comparative alloys. Nominal 300 lb. (136kg) heats were induction melted under a partial pressure of nitrogen gasand then atomized with nitrogen gas. The resulting metal powder of eachheat was screened to −40 mesh, blended, and then filled into an 8 in.round×23 in. long (20.3 cm×58.4 cm) mild steel can. The cans were vacuumoutgassed at 400° F. (703° C.) and then hot isostatically pressed(HIP'd) at 15 ksi (103.4 MPa) for 4-5 hours at a temperature of 2050° F.(1121° C.). The as-HIP'd cans were forged to 5½ in. (14 cm) doubleoctagon billets from a forging temperature of 2100° F. (1149° C.). Thedouble-octagonal billets were vermiculite cooled, stressed relieved at1400° F. (760° C.) for 6 hours, and then cooled in air. Thestress-relieved billets were rotary forged to 4 in. (10.2 cm) round barsfrom a forging temperature of 2100° F. (1149° C.). The as-forged barswere stress relieved at 1400° F. (760° C.) for 4 hours and then cooledin air. The bars were then further annealed at 1616° F. (880° C.) for 8hours, cooled at 18° F. /hour (10° C. /hour) to 1202° F. (650° C.), andthen furnace cooled.

Standard size cube specimens for Rockwell hardness testing were cut fromthe annealed bar of each heat. The cube samples were preheated for 5minutes in salt at 1600° F. (871° C.), austenitized in salt at 2250° F.(1232° C.) for 3 minutes, and then quenched in oil. One set of cubes wastempered at 1000° F. (538° C.) for 2 hours and another set of cubes wastempered at 1025° F. (552° C.) for 2 hours. After tempering all cubeswere cold treated at −100° F. (−73.3° C.) for 1 hour and then warmed inair to room temperature. The first set of cubes was then tempered at1000° F. (538° C.) for 2 hours+2 hours and the second set of the cubeswas tempered at 1025° F. (552° C.) for 2 hours+2 hours. The 2250° F.(1232° C.) austenitization temperature was selected to provide maximumsolutioning of the alloy while still being a commercially feasibleprocess. The cold treating and triple tempering are used to minimize theamount of any austenite retained in the alloy after austenitization. The1000° F. (538° C.) tempering temperature was selected to provide maximumhardness in this alloy, whereas the 1025° F. (552° C.) temperingtemperature was selected to provide better toughness in the alloy,although at a slightly lower hardness level.

Set forth in Table 3 below are the results of room temperature hardnesstesting on the as-tempered samples from each heat. The results are givenin Rockwell C-scale (HRC) and represent the average of 5 readings takenon each sample.

TABLE 3 Temper Ex. Ex. Ex. Ex. Ex. Ex. Ht. Ht. Ht. Ht. Ht. Temp. 1 2 3 45 6 A B C D E 1000° F. 69.5 69.5 70.0 69.5 70.0 70.5 68.0 69.0 69.0 68.567.5 (538° C.) 1025° F. 69.5 69.5 69.5 69.5 70.0 70.0 68.5 69.0 69.068.5 68.5 (552° C.)

Test samples measuring 1in.×2in.×3in. (2.5 cm×5.1 cm×7.6 cm) were cutfrom the annealed bar of each heat for hot hardness testing. Thesesamples were hardened and tempered utilizing the same heat treatment asused for the room temperature hardness test samples. However, thespecimens for this test were tempered only at 1025° F. (552° C.). Setforth in Table 4 below are the results of the hot hardness testing ofeach of the samples. The hardness values were measured while thespecimen was maintained at a temperature of 1000° F. (538° C.). Brinellhardness testing was used for this test and the Brinell hardness valueswere converted to HRC. The results are given in Rockwell C-scale (HRC)and represent the average of 2 readings taken on each sample.

TABLE 4 Ex. Ex. Ex. Ex. Ex. Ex. Ht. Ht. Ht. Ht. Ht. 1 2 3 4 5 6 A B C DE HRC 61.0 63.0 61.0 60.0 62.0 62.5 58.0 58.0 62.5 62.0 62.0

To be useful as a high speed tooling material for the more-demandingrequirements of the machine tool industry, a high speed tool steel alloyshould provide a hardness of at least about 70 HRC. For practicalpurposes a hardness of bout 69.5 HRC is considered acceptable whentaking into account the expected variation in test blocks and theaccuracy of the known testing machines at the desired hardness level.The data in Table 3 clearly show that Examples 1-6 of the alloyaccording to the present invention provide the desired level of roomtemperature hardness at each tempering temperature whereas none of HeatsA-E was able to achieve the desired level of hardness. The data in Table4 show that the examples of the alloy according to this inventionconsistently provide a hot hardness of greater than 60 HRC, whereas someof the comparative heats did not.

Another important aspect of the alloy according to the present inventionis that it provides acceptable toughness at the significantly higherhardness that is characteristic of the alloy. To demonstrate the goodtoughness provided by this alloy, Izod testing was performed onstandard, unnotched Izod test samples cut from the bars of each heat.The test samples were cut with a longitudinal orientation. The Izod testsamples were hardened and tempered in the same manner as the roomtemperature hardness specimens described above. The hardness of eachtest sample was also determined Shown in Tables 5A and 5B are theresults of room temperature testing including the Rockwell hardness(HRC) of each test specimen (HRC) and the Izod impact toughness inft.-lbs (J). Table 5A shows the results for the specimens tempered at1000° F. (538° C.) and Table 5B shows the results for the specimenstempered at 1025° F. (552° C.). Triplicate specimens of each compositionwere tested and the individual impact toughness results are reportedtogether with the average thereof. The Izod test can have a significantvariance between individual readings. Therefore, it is appropriate toconsider average values when comparing results.

TABLE 5A Impact Toughness Ex./Ht. HRC Individual Avg. 1 69.5 12.0, 11.0,11.5 11.5 (16.3, 14.9, 15.6) (15.6) 2 69.5 7.5, 5.5, 6.5 6.5 (10.2, 7.5,8.8) (8.8) 3 69.5 4.0, 1.0, 7.5 4.2 (5.4, 1.4, 10.2) (5.7) 4 69.5 3.0,6.0, 7.0 5.3 (4.1, 8.1, 9.5) (7.2) 5 70.0 6.5, 8.0, 5.5 6.7 (8.8, 10.8,7.5) (9.1) 6 70.0 6.0, 7.0, 4.0 5.7 (8.1, 9.5, 5.4) (7.7) A 68.5 19.0,20.0, 13.5 17.5 (25.7, 27.1, 18.3) (23.7) B 69.0 7.5, 16.5, 17.0 13.7(10.2, 22.4, 23.0) 18.6) C 69.0 7.5, 14.5, 8.5 10.2 (10.2, 19.7, 11.5)(13.8) D 68.0 7.0, 8.0, 8.0 7.7 (9.5, 10.8, 10.8) (10.4) E 67.5 7.0,3.5, 7.0 5.8 (9.5, 4.7, 9.5) (7.8)

TABLE 5B Impact Toughness Ex./Ht. HRC Individual Avg. 1 69.5 9.0, 8.0,8.0 8.3 (12.2, 10.8, 10.8) (11.3) 2 69.5 13.0, 8.0, 10.5 10.5 (17.6,10.8, 14.2) (14.2) 3 69.5 5.0, 6.0, 11.5 7.5 (6.8, 8.1, 15.6) (10.2) 469.5 8.0, 8.0, 13.5 9.8 (10.8, 10.8, 18.3) (13.3) 5 70.0 5.0, 5.0, 5.55.2 (6.8, 6.8, 7.5) (7.1) 6 70.0 6.5, 4.0, 4.5 5.0 (8.8, 5.4, 6.1) (6.8)A 68.5 16.5, 16.0, 20.0 17.5 (22.4, 21.7, 27.1) (23.7) B 69.0 11.5,12.0, 12.0 11.8 (15.6, 16.3, 16.3) (16) C 69.0 9.5, 4.0, 6.5 6.7 (12.9,5.4, 8.8) (9.1) D 68.0 8.0, 5.5, 6.0 6.5 (10.8, 7.5, 8.1) (8.8) E 67.54.0, 6.0, 4.0 4.7 (5.4, 8.1, 5.4) (6.4)

Acceptable toughness for a high hardness, high speed tool steel alloy,such as that according to the present invention, is indicated by an Izodimpact toughness value of at least 6 ft.-lbs (8.1 J) for materialtempered at 1000° F. (538° C.) or by a value of at least 7 ft.-lbs. (9.5J) for material tempered at 1025° F. (552° C.). Although those thresholdvalues are somewhat lower than the impact toughness levels provided bythe known high speed tool steel alloys, it is important to note that theknown alloys do not provide the very high hardness provided by the alloyof this invention. Furthermore, the threshold values are significantlybetter than the toughness provided by cemented carbide tool materialswhich do provide very high hardness levels. It is also important to notethat the toughness of a high speed tool steel alloy after tempering at1025° F. (552° C.) is of greater significance because from thecommercial perspective, most tool fabricators use a temperingtemperature of 1025° F. (552° C.) or higher in order to obtain bettertoughness in the tools and to obtain a higher working temperature rangefor the tools.

When considered as a whole, the data in Tables 5A and 5B show thatexamples of the alloy according to the present invention provide asuperior combination of hardness and toughness compared to the heats ofthe other alloy compositions. The data in Table 5A show that Examples 1,2, and 5 meet or exceed the 6 ft.-lb. (8.1 J) minimum Izod impacttoughness criterion at a significantly higher hardness level than any ofcomparative Heats A to D. Since high hardness is a primary requirementof high speed tool materials, Examples 3, 4, and 6 would be acceptablecompositions for tooling applications where toughness is not asignificant concern. Heat E does not meet either the minimum hardnesscriterion or the minimum toughness criterion. The data in Table 5B showthat Examples 1, 2, 3, and 4 meet or exceed the 7 ft.-lb. (9.5 J)minimum Izod impact toughness criterion at a significantly higherhardness level than either of comparative Heats A or B. Heats C, D, andE do not meet either the minimum hardness criterion or the minimumtoughness criterion.

The terms and expressions which have been employed herein are used asterms of description, not of limitation. There is no intention in theuse of such terms and expressions of excluding any equivalents of theelements or features shown and described or portions thereof. However,it is recognized that various modifications are possible within thescope of the invention claimed.

What is claimed is:
 1. A tool steel alloy having a unique combination ofhardness and toughness, said alloy consisting essentially of, in weightpercent, about: wt. % C 1.85-2.30 Mn 0.15-1.0  Si 0.15-1.0  P 0.030 max.S   0-0.30 Cr 3.7-5.0 Ni + Cu  0.75 max. Mo  1.0 max. Co  6-12 W12.0-13.5 V 4.5-7.5

and the balance is essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that −0.05≦ΔC≦−0.42 whereΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C.
 2. The tool steel alloy setforth in claim 1 which contains at least about 1.90% carbon.
 3. The toolsteel alloy set forth in claim 1 which contains at least about 4.0%chromium.
 4. The tool steel alloy set forth in claim 1 which contains atleast about 7% cobalt.
 5. The tool steel alloy set forth in claim 1which contains at least about 12.25% tungsten.
 6. The tool steel alloyset forth in claim 1 which contains at least about 5.0% vanadium.
 7. Thetool steel alloy set forth in claim 1 which contains not more than about0.06% sulfur.
 8. A tool steel alloy having a unique combination ofhardness and toughness, said alloy consisting essentially of, in weightpercent, about: wt. % C 1.90-2.20 Mn 0.15-0.90 Si 0.50-0.80 P 0.030 max.S   0-0.30 Cr 4.0-5.0 Ni + Cu  0.50 max. Mo  1.0 max. Co  7-11 W12.25-13.5  V 5.0-7.0

and the balance is essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that  −0.10≦ΔC≦−0.35where ΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C.
 9. The tool steel alloyset forth in claim 8 which contains at least about 4.25% chromium. 10.The tool steel alloy set forth in claim 8 which contains at least about7.5% cobalt.
 11. The tool steel alloy set forth in claim 8 whichcontains at least about 12.5% tungsten.
 12. The tool steel alloy setforth in claim 8 wherein −0.15≦ΔC≦−0.25.
 13. The tool steel alloy setforth in claim 8 which contains not more than about 0.06% sulfur.
 14. Atool steel alloy having a unique combination of hardness and toughness,said alloy consisting essentially of, in weight percent, about: wt. % C1.90-2.20 Mn 0.15-0.90 Si 0.55-0.75 P 0.030 max. S   0-0.30 Cr 4.25-5.00Ni + Cu  0.50 max. Mo  1.0 max. Co  7.5-10.5 W 12.5-13.5 V 5.0-6.5

and the balance is essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that −0.15≦ΔC≦−0.25 whereΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C.
 15. The tool steel alloy setforth in claim 14 which contains not more than about 0.06% sulfur.
 16. Apowder metallurgy tool steel article having a unique combination ofhardness and toughness said article being made from consolidated alloypowder having the following weight percent composition: wt. % C1.85-2.30 Mn 0.15-1.0  Si 0.15-1.0  P 0.030 max. S   0-0.30 Cr 3.7-5.0Ni + Cu  0.75 max. Mo  1.0 max. Co  6-12 W 12.0-13.5 V 4.5-7.5

and the balance essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that −0.05≦ΔC≦−0.42 whereΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C said article, when heattreated, provides a Rockwell C hardness of at least about 69.5.
 17. Atool steel article as set forth in claim 16 wherein the alloy powdercontains about 1.90-2.20% carbon.
 18. A tool steel article as set forthin claim 16 wherein the alloy powder contains about 4.0-5.0% chromium.19. A tool steel article as set forth in claim 16 wherein the alloypowder contains about 7-11% cobalt.
 20. A tool steel article as setforth in claim 16 wherein the alloy powder contains about 12.25-13.5%tungsten.
 21. A tool steel article as set forth in claim 16 wherein thealloy powder contains about 5.0-7.0% vanadium.
 22. A tool steel articleas set forth in claim 16 wherein the alloy powder contains not more thanabout 0.06% sulfur.
 23. A powder metallurgy tool steel article having aunique combination of hardness and toughness, said article being madefrom consolidated alloy powder having the following weight percentcomposition: wt. % C 1.90-2.20 Mn 0.15-0.90 Si 0.50-0.80 P 0.030 max. S  0-0.30 Cr 4.0-5.0 Ni + Cu  0.50 max. Mo  1.0 max. Co  7-11 W12.25-13.5  V 5.0-7.0

and the balance essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that −0.10≦ΔC≦0.35 whereΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C said article, when heattreated, provides a Rockwell C hardness of at least about 69.5.
 24. Atool steel article as set forth in claim 23 wherein the alloy powdercontains about 4.25-5.00% chromium.
 25. A tool steel article as setforth in claim 23 wherein the alloy powder contains about 7.5-10.5%cobalt.
 26. A tool steel article as set forth in claim 23 wherein thealloy powder contains about 12.5-13.5% tungsten.
 27. A tool steelarticle as set forth in claim 23 wherein the alloy powder contains about5.0-6.5% vanadium.
 28. A tool steel article as set forth in claim 23wherein the alloy powder contains not more than about 0.06% sulfur. 29.A powder metallurgy tool steel article having a unique combination ofhardness and toughness made from consolidated alloy powder having thefollowing weight percent composition: wt. % C 1.90-2.20 Mn 0.15-0.90 Si0.55-0.75 P 0.030 max. S   0-0.30 Cr 4.25-5.00 Ni + Cu  0.50 max. Mo 1.0 max. Co  7.5-10.5 W 12.5-13.5 V 5.0-6.5

and the balance essentially iron and usual impurities, wherein theelements C, Cr, Mo, W, and V are balanced such that −0.15≦ΔC≦−0.25 where ΔC=((0.033W)+(0.063Mo)+(0.06Cr)+(0.2V))−C said article, when heattreated, provides a Rockwell C hardness of at least about 69.5.
 30. Atool steel article as set forth in claim 29 wherein the alloy powdercontains not more than about 0.06% sulfur.